Declutterers - a book recommendation

Books weren't that hard for me as I was already listening to audiobooks by then and most of the books I had were there just because I've never got rid of them rather than because I really wanted to keep them.

I kept one shelf of fiction because I either really loved the story - or because the book was somehow special to me - one signed by the author that a friend got especially for me, the last book my Dad & I both read etc.
The rest I gave to friends, and like others dropped off to various "little libraries" or thrift stores
I got rid of most of my cookbooks, I look up 80% of recipes online now anyway, again, I kept 6...4 bakery books, 1 when I met the author & he wrote me a message in it and one I still use a bit.
I also kept several coffee table art books because I still enjoy looking through them, and they live on the same shelf as the photobooks I've created over the years. 
That was just what I did.

Now if you are on a decluttering thread it means you must have more books than you can store comfortably and they are taking up space in other areas of your home that you need for something else.
What this author says is that our homes are where we live and so we need to be able do our "living" there - have friends over, cook meals, play games, sit in a corner and read etc etc...if we have so much stuff in there that we can't comfortably move around and do the living we want to do - then we do NOT need to get a bigger house, we just need to get rid of the extra stuff to make the house we already have more functional.

Her theory is that we need to keep the books somewhere - so obviously a bookshelf that is an appropriate size for your home. Put all the books you love/need/want to read MOST in first. The bookshelf is the container, it's there to store the books, but also acts as a realistic limit for your book collection.
Once the 'container' is full...there's no more room and all the books that aren't in it need to go.
Put them into a donate box- and donate them asap.
If as you put them in the donate box you see one you must keep - then that's OK - but one you love less needs to be taken off the shelf to make room.
Once you've done that, then in the future for each book you bring home - one needs to be go.

So the decluttering decision isn't about books you won't read, or books you don't like...yes you might well read every single book eventually, BUT if there isn't enough room in your house to store the books in space you have available (the bookshelf) then you put in the most important ones until the space is full...and you need to get rid of the rest. 
That mindset should also stop you buying so many books in the future because you know it means you'll have to come home and get rid of one.
And if you want to buy 100 new books and not worry about storage - then get an e-reader!

That's what resonates with me in her approach, she's not trying to convince us to be minimalists or that it's bad to have things...what she's doing is pointing out that if we want to live in a non cluttered functional/livable house, then we need to respect the limits of our storage capacity in each area.

That's the part this author doesn't like and for me - she's right.
That's how I ended up with 3 boxes of "to keep" stuff that doesn't have a home.
Deciding to keep it when I don't have enough space for it...that's my problem. I need to find a way not to do that and realise I need to get rid of it the first time around.

It sounds to me like you aren't the one who actually clutters up the spaces...you're the one who cleans up after the other clutterers.